California replaces Arizona in cotton pest control treatments

California cotton farmers now treat more often for pests than Arizona producers, according to veteran Arizona pest control adviser Art Anderson of Phoenix, sales rep for Valent.

California has never seen the hordes of major pest problems like Arizona where a succession of pest invasions of pink bollworm, boll weevil and silverleaf whitefly have more than once threatened the demise of the state’s cotton. Fortunately, Arizona has turned back each assault and now growers there, according to Anderson, treat for insect pests on the average of only one to three times per season. Anderson told a group of consultants and producers recently at a Valent-sponsored meeting at Harris Ranch in Coalinga, Calif., that California producers now treat an average of four to six times.

This year it could be considerably more as pest control advisers report high levels of worms and now aphids and silverleaf whiteflies are reported to be increasing in the valley. Lygus did not materialize as predicted, but other pests have taken its place as threats to this year’s crop.

It has been a remarkable turnaround for Arizona where growers in the past had to resort to weekly and often more frequent pesticide applications to protect crops against pests.

Bt cotton credited

A major reason for the turnaround has been the development of Bt cotton. Anderson said 70 percent of Arizona’s 2003 crop is Bollgard cotton this season. Since introduced a decade ago, the threat of pink bollworm to the state’s cotton has virtually disappeared. Before BT cotton, growers were forced to spray pesticides to control pink bollworm. That often set off a chain reaction of other pests threatening cotton.

The current generation of Bt cotton controls only pink bollworm, which is not a major pest in California cotton thanks to a grower-funded sterile release program which has kept PBW out of the San Joaquin Valley for more than three decades.

However, a second generation of Bt cotton promises to give control or suppression of beet armyworm, loopers and other worm pests not now controlled by Bollgard cottons. This new technology is gaining interest in California as worm pressure increases.

The last major pest outbreak in Arizona was the silverleaf whitefly, which not only devastated the crop in the field in the mid 1990s, but also created sticky cotton problems.

Once again, Arizona producers turned back the pest with innovative pest management techniques that included a pair of early season inspect growth regulators (IGR).

One is Knack. The other is Courier (formerly known as Applaud).

Knack from Valent has been applied to Arizona cotton since 1996 "We are in our eighth year and have never seen a failure," said Anderson.

Once per season

The primary reason for that is that the product is labeled by Valent for only one application per season and only on cotton in Arizona. This is to ward off whitefly resistance to the IGR.

"From the first year we registered Knack for Arizona, we pledged not to register it for more than one use per season and we have not registered it on other crops," said western sales manager Mark Testerman. "We want the product to be around for a long time."

While product failures have not been reported, Anderson warned that waiting too late to treat can result in less than desirable results.

The reason Anderson was detailing the use of Knack in Arizona is because California now faces the constant threat of silverleaf whitefly problems. This year, said Testerman, he expects the problems to be significant in the San Joaquin Valley.

The crop is late and growers have been forced to treat for worms, oftentimes reducing beneficial insects. This has spawned aphid problems and the lateness of the crop is increasing the whitefly threat. Whiteflies and aphids have been implicated in lint stickiness that became a major marketing problem for SJV cotton two years ago.

The problem prompted California Cotton Growers Association and the University of California to mount an aggressive no-stickiness educational effort to prevent the problem from happening again. This year is expected to be the biggest challenge since that campaign began.

"We sold more Knack in California last year than we did in Arizona, and we expected see a big increase this year from last in California," said Testerman. "Arizona growers are seeing more whitefly earlier, but they are getting on it pretty good."

Anderson said the desert crop was late getting started just like it was in California, but the Arizona crop has caught up and is now seven to 10 days ahead of the 2002 crop.

Unseasonably hot

It has been unseasonably hot this summer even by Arizona standards. In hot weather the whitefly is capable of completing its life cycle quicker. This increases population levels. One of the challenges in whitefly control is unless it is controlled early, populations of overlapping generations can build. It is more difficult to control adults than early-season nymphs.

Anderson said Knack can give up to 45 days of early-season control if applied early enough to control nymphs. Knack does not control adult whiteflies.

The insect growth regulator (IGR) acts by suppressing embryogenesis within the insect egg and by inhibiting metamorphosis and adult emergence. While it will not kill adults, eggs hatched by treated adults will be suppressed.

The University of Arizona developed scouting guidelines to determine when to use an IGR. Entomologists there recommend using the fifth main stem node leaf for sampling, counting only large, visible nymphs on at least 30 leaves. Knack is recommended when whiteflies reach threshold levels of three to five adults per leaf or the equivalent of immatures.

Anderson also suggested PCA check for whiteflies in the lower canopy since the pest will move down in hot weather.

Anderson acknowledged Knack is an expensive product, but cutting the recommended rate of six to 10 ounces is not wise. All that will do is compromise control and could lead to resistance development, he said.

"Resistance can happen. We have seen resistance in greenhouses, but we do not want to see it in cotton," said Anderson.

Control strategy

UA entomologists developed a strategy for whitefly control if the problem persists beyond the window of control from the IGRs. Stage II involves the use of non-pyrethroid pesticides like Provado, endosulfan and Vydate and if late season control is necessary, UA has developed a Stage III strategy that includes pyrethroids, organophosphates and carbamates.

"From the way things are shaping up this year, I suspect we will see growers resorting to Stage II-type whitefly management strategies in California with the nicotinyl products," said Testerman.

Danitol from Valent is a compound that was used late against whitefly in California last season. It must be tank mixed with another product like Ortheme, Curacron, endosulfan, Monitor or Lorsban for acceptable control during the growing season. However, Danitol can be added alone to defoliants.

"We saw growers use it last year in defoliants to clean up whitefly to keep lint clean until harvest, and I suspect we will see it used more widely this season," he added.